Storage of biological and chemical samples is becoming widespread in the biotechnology and medical industries. To preserve many of these samples, the samples must be stored well below normal freezing temperatures. Generally speaking, a regular freezer operates from −5° C. to −20° C., an ultra-low temperature freezer operates from about −50° C. to −130° C. (preferably at about −80° C.) and a cryogenic freezer operates from about −140° C. to −196° C. (the boiling point of liquid nitrogen). The present invention is directed to a large automated storage and retrieval system containing one or more ultra-low temperature or cryogenic freezer bays operating below about −65° C. The freezers are contained within a refrigerated enclosure, preferably maintained at about −20° C.
Most biological samples stored in ultra-low temperature or cryogenic systems are contained in sealed plastic laboratory tubes held in tube storage racks in arrays of, for example, 48, 96 or 384 tubes. In some cases, a two dimensional barcode is adhered to the bottom of the tubes and is able to be read through the bottom of the storage racks. In other cases, a one dimensional barcode is placed on the side of the wall of the tube. It is also typical for the sample storage racks themselves to have a barcode. In all cases, bar coding facilitates data entry into a control system that keeps track of the location of each of the biological samples. In some applications, samples are stored in sample storage plates such as sealed microtitre plates or wellplates, rather than stored in sealed tubes held in a rack.
In the art, it is known to store tube storage racks or plates on vertical shelves in cassettes or in drawers in ultra-low temperature or cryogenic freezer chests, which in turn are located within a refrigerated (e.g., −20° C.) work space. In these systems, active robotic equipment operates in the −20° C. environment to pull the tube storage racks or plates from the ultra-low temperature or cryogenic freezer(s) for sample retrieval and placement. The present invention is directed primarily to an automated rack robot for transporting sample storage tube racks or plates in the −20° C. environment within the system after the cassette of racks or plates has been pulled from a bank of ultra-low temperature or cryogenic freezer chests. The preferred cassette puller is designed according to U.S. patent application Ser. No. 13/228,651, entitled “Cassette Puller”, Publication No. US2012/0060539A1 (now abandoned) filed on Sep. 9, 2011, and incorporated herein by reference, and is also designed to accommodate storage cassettes as described in co-pending U.S. patent application Ser. No. 13/228,662, entitled “Sample Storage Cassette for Ultra-Low or Cryogenic Temperatures”, Publication No. US2012/0060541A1 filed on Sep. 9, 2011, also incorporated herein by reference. The preferred cassette puller includes an insulated sleeve into which a cassette is pulled from the freezer and then ejects a selected tube storage rack or plate onto an ejector plate or onto an alternative staging area outside of the sleeve to present the rack or plate within the −20° C. environment for processing.
One of the primary purposes of the rack robot is to reliably lift and transfer tube storage racks or plates within the warmer −20° C. environment for processing, e.g. from the cassette puller to a tube picking station, a barcode reading station, a frost removal station, or other location, or for returning the rack or plate to the ultra-low temperature or cryogenic freezer. For example, placement of racks or plates, or tubes within tube racks may not be as expected or precise for a number of reasons such as frost accumulation or other physical contingencies. In this regard, an objective of the invention is to ensure that tubes are in place in racks and that racks or plates are secure prior to lifting and transfer with the rack robot. In addition, it has been found that the speed at which the rack robot operates is often a throughput bottleneck and slows overall operation of the system. Therefore, another objective of the invention is to minimize the time necessary to reliably lift and transfer plates or racks. Further, another objective of the present invention is to limit undesirable sample temperature rise when transferring samples within the warmer −20° C. environment, which is, e.g., about 60° C. warmer than the freezer temperature in a system with ultra-low temperature (−80° C.) freezers.